A silicone hydrogel contact lens has been known as one kind of contact lens. The silicone hydrogel contact lens has been expected to suppress eye diseases resulting from the oxygen deficiency of a cornea, such as an infectious disease, corneal vascularization, and corneal endothelial cell damage, because the lens has oxygen permeability drastically higher than that of a related-art contact lens. Meanwhile, silicone is a material having extremely strong hydrophobicity, and hence has involved a problem in that when the silicone is used as it is as a contact lens, corneal damage due to a tear breakup or friction with an ocular tissue in association therewith occurs. In view of the foregoing, companies developing silicone hydrogel lenses have been modifying the surfaces of the lenses through various methods to transform their physical properties into those applicable to eyes.
As a method of modifying the surface of a contact lens, a method involving using graft polymerization has already been known in the art. In Patent Literature 1, there is a description of a method involving subjecting the surface of a polysiloxane contact lens to graft polymerization with N,N-dimethylacrylamide to improve the hydrophilicity of the surface of the contact lens while maintaining its oxygen permeability.
In Patent Literature 2, there is a description of a method involving subjecting the surface of a base material, such as a polysiloxane, to graft polymerization with methacrylic acid, sodium methacrylate, sodium vinyl sulfonate, or sodium styrene sulfonate to improve the hydrophilicity of the surface of the base material.
In Patent Literature 3, there is a description of a method involving subjecting a silicone hydrogel base material to graft polymerization with a special zwitterionic group-containing monomer to improve the hydrophilicity and lubricity of the surface of the base material.
In Patent Literature 4, there are descriptions of a method involving mixing a water-soluble polymer, which is obtained by polymerizing a polyoxyethylene compound having a free radical-polymerizable group and having a weight-average molecular weight of from about 300 to about 500, into the package preservation solution of a hydrogel lens in advance, and treating the mixture with an autoclave to cause the polymer to physically adhere to the surface of the lens, and a method involving dissolving the water-soluble polymer in a monomer mixture in advance, and polymerizing the monomer mixture to provide a lens, thereby modifying the surface of the lens.
However, a method involving improving the hydrophilicity of the surface of a silicone hydrogel lens with a polyoxyethylene derivative having a branched chain length has not been known yet.